A multiple disc clutch mechanism is mainly composed of a bottomed cylindrical clutch guide and a clutch hub arranged concentrically inside the clutch guide. On one hand, a plurality of separator plates (friction materials) is attached on an inner periphery of the clutch guide due to spline fitting (connection). On the other hand, on an outer periphery of the clutch hub, a plurality of friction plates (friction materials) is attached alternately with the separator plates due to spline fitting. For example, refer to Patent Document 1.
Moreover, the multiple disc clutch mechanism includes a hydraulic piston for applying a pressing force to a laminate (frictional engagement member) of the separator plates and the friction plates for press-fitting the laminate and a piston chamber for driving the hydraulic piston. Accordingly, hydraulic fluid (oil) is supplied to the piston chamber to drive the hydraulic piston in the axial direction, and thus the hydraulic piston presses the frictional engagement member in the axial direction. Thus, a torque is transmitted between the clutch guide side and the clutch hub side. Transmission torque capacity of the multiple disc clutch mechanism varies depending on a fastening degree of the frictional engagement member. Therefore, a pressing load receiving member for receiving the pressing force of the hydraulic piston is provided at a rear of the clutch guide so that the pressing force applied by the hydraulic piston is efficiently transmitted to the frictional engagement member.
In addition, a hydraulic control device (hydraulic control circuit) is known as a hydraulic control circuit for supplying oil to the multiple disc clutch mechanism. This hydraulic control device includes an oil strainer for storing oil an electric oil pump for pumping up and forcibly feeding the oil from the oil strainer to an oil passage, a piston chamber for driving the hydraulic piston for engaging a clutch, a linear solenoid valve provided downstream of the piston chamber for adjusting pressure of the hydraulic fluid to a predetermined pressure, an outgoing oil passage leading to the piston chamber from the electric oil pump and an incoming oil passage leading to the linear solenoid valve from the piston chamber. For example, see Patent Document 2.
In the hydraulic control circuit described in Patent Document 2, the oil pumped up from the oil strainer by the electric oil pump is supplied to the piston chamber of the hydraulic piston via the outgoing oil passage, and then supplied to the linear solenoid valve via the incoming oil passage from the piston chamber. After adjusted here to the predetermined hydraulic pressure, the oil is partly returned to the oil strainer, and the remainder thereof is supplied for lubrication to a rotation sliding member such as a bearing and a clutch. Further, the linear solenoid valve is stored in a case called “hydraulic control body” as the linear solenoid valve is controlled by a computer on the basis of a signal output from an oil pressure sensor.
In the above-described hydraulic control circuit, the piston chamber of the hydraulic piston is provided at a shaft end of a farthest clutch from the hydraulic control body. This causes the problem that the oil passage from the piston chamber to the hydraulic control body becomes long along with a large pressure loss.
As the downstream from the linear solenoid valve is atmospherically released, a pressure loss from the piston chamber to the linear solenoid valve acts as an operating pressure on the piston chamber.
In particular, due to higher viscosity of the hydraulic fluid at an ultralow temperature, the pressure loss in the oil passage grows larger, and consequently, the pressure loss generates a clutch operating pressure also at an instructed oil pressure of zero (in the state of linear solenoid full opening). This results in clutch dragging, which might cause problems such as impacting on vehicle behavior due to transmission of a driving force to rear wheels and deteriorating fuel consumption rate.
Moreover, the oil pressure transmission device described in Patent Document 1 performs shaft core lubrication of a rotation sliding member such as a bearing and a clutch by supplying oil via an oil passage (shaft core oil passage) formed inside a center shaft. In this shaft core lubrication, a hydraulic control body is arranged above the center shaft and in the vicinity of the center of the device so that lubrication oil is equal in quantity between left and right clutches.
As described in Patent Document 1, a taper roller bearing or an angular ball bearing is used as a bearing for the center shaft to which a hypoid gear is spline-coupled for transmitting a driving force approximately at a right angle. Conventionally, for the improvement of assemblability, these bearings having an additional tightening margin are fixed to a case using a ring member (bearing set plate) whose central part is opened.
In the case of the shaft core lubrication in which the hydraulic control body is arranged above the center shaft and in the vicinity of the center of the device, flexibility as to where the pressing load receiving member for receiving a pressing force of the hydraulic piston is arranged depends on where the hydraulic control body is arranged. As a result, the pressing load receiving member is arranged so as to be offset to a pressing position of the hydraulic piston, whereby the thrust efficiency of the hydraulic piston at the time of clutch engagement deteriorates and the transmission torque capacity of the clutch might fall below a required amount.
The bearing set plate for adding a tightening margin to the taper roller bearing, etc. is fastened and fixed to the case by a volt.
However, the arrangement of the volt restricts the flexibility as to where to arrange the pressing load receiving member. Consequently, similar to the arrangement of the hydraulic control body, the pressing load receiving member is offset to a pressing position of the hydraulic piston, whereby the transmission torque capacity at the time of clutch engagement might fall short of the required amount.